Many industrial plants, such as continuous material processing lines, comprise machinery with movable members that represent a serious danger for the operators if the operators approach the machines when they are running.
However, it is often necessary to make interventions on the machinery, both for maintenance reasons and for performing certain steps of the production or processing cycle, for example to eliminate the cause of a temporary stop of the line. These interventions require that one or more operators move towards the machinery. To avoid accidents, which could have serious and even very serious consequences, it is often necessary to allow the access to the dangerous machinery areas only when the machinery is idle, or is in a safety condition, i.e. a condition different than the normal operating condition.
For instance, in lines for processing continuous web materials, such as paper webs, for producing rolls or other articles starting from a continuous article, different stations are provided in sequence along the processing line. Each station has one or more machines with moving members, performing operations on the continuous web material. Typically, in tissue paper processing for producing rolls, lines are provided comprising one or more unwinders that unwind respective parent reels of great dimensions in order to feed one or more subsequent processing stations. Downstream of the unwinders, embossing units, printing units, perforating units may be provided, as well as a rewinding machine, a tail sealer or other machine for closing the tail end of the rolls formed by means of the rewinding machine.
In lines for producing articles of folded paper, embossing and/or printing units, as well as cutting and folding stations and the like may be provided downstream of one or more unwinders.
Access areas are usually provided between adjacent stations for the access of maintenance operators or other operators in charge of managing the production operations. These operations may be, for instance, recovery operations in case of breakage of the web material, or replacement of exhausted parent reels with new reels.
In many cases, a leading edge of the material shall be inserted in the web material feeding path. This occurs, for example, in case of accidental breakage of the web material due to a malfunction of the line or other unforeseen events.
In some cases, the insertion of the leading edge of the web material through the feeding path is called threading. To thread the leading edge along the feeding path, the various machines arranged in sequence are made operate slowly and partially, by activating at low speed only the members useful for feeding the leading edge of the web material. Generally, during threading it is not necessary to activate all the members of the machines. Typically, in case of embossing or printing units, the gluing systems, the mechanical bonding systems, if any, the perforating units and the printing units may remain idle. This operating mode, wherein the machinery runs only partially and at slow speed, sometimes in an intermitting way, is also called jog.
These threading interventions or other interventions on the machines forming the stations of a processing line require that the operators access risk areas arranged near the machines or, in some cases, along the path of the material to be processed, and therefore between one station and the subsequent one, or between machines of a same station.
In order to reduce the risk of accidents, the risk areas are closed by means of safety gates. In order to open these safety gates and access the respective risk areas, at least the machines adjacent to the risk areas shall be in a safety condition, typically in a condition of stop. Usually associated with the gates are micro-switches, which cause the stop of the line or part of the line if the gate opens.
In some cases, the interventions on the line require that operators access more risk areas one after the other, with the consequent need of repeated operations for opening and closing the safety gates.
These known systems controlling the access to the risk areas are not satisfactory from a safety point of view, as they do not allow to ensure that all operators have left the risk areas before restarting the machines or the line. While to access a risk area it is necessary to stop the machines near this area, or the whole line (otherwise the safety gate does not open), to restart the line or the machines it is only necessary that the safety gate closes again. If the safety gate is closed when an operator is still in the risk area, very dangerous situations may occur, i.e. very risky situations for the operator, as the machines may be restarted even if there are people in the risk area.
A need therefore exists for systems controlling the access to potentially dangerous processing machines, which are more reliable and allow easier interventions and access.